Support base



FIG. 1 is a perspective view of a support base embodying the design of the invention;

FIG. 2 is a top plan view of the support base;

FIG. 3 is a front elevational view of the support base, of which the back elevational view is a mirror image;

FIG. 4 is a left elevational view of the support base, of which the right elevational view is a mirrror image; and,

FIG. 5 is a bottom plan view of the support base. 

The ornamental design for a support base, as shown and described. 